The prevalence of obstructive sleep apnea (OSA) in adults in Western countries is growing at an exponential rate, with as many as 50% of middle-aged males and 20% of middle-aged females have at least mild sleep disordered breathing. OSA is characterized by periodic, partial or complete obstruction of the upper airway during sleep. The underlying pathophysiology of OSA is complex. However, it is generally accepted that the stability and patency of the upper airway is dependent upon the action of oropharyngeal dilator muscles which are normally activate during inspiration. These muscles increase activity to overcome obstruction during wakefulness, but the normal decrease in activity that occurs during sleep leaves the airway susceptible to collapse. Return of airway muscle activity requires either an arousal or a change of brain state to a lighter stage of sleep. Given the choice between sleeping and breathing, the un-medicated brain will choose breathing. The repetitive asphyxia causes repetitive arousals which fragments sleep and causes daytime somnolence. Airway obstruction also causes sleep-associated oxygen desaturation, episodic hypercarbia, and cardiovascular dysfunction.
The most common method used to treat OSA is through the application of continuous positive airway pressure (CPAP). An alternative approach, called oral appliance therapy (OAT), protrudes the mandible in a forward position thereby reducing obstruction during sleep caused by the tongue and linked soft tissues. OAT is considered limited when compared to CPAP because it is not effective in all patients. Efficacious OAT outcomes is dependent on a number of factors, including but not limited to a patient's gender, supine and non-supine OSA severity, age, body mass index, neck size and the anatomical source/region of obstruction. Successful outcomes are also influenced by two factors which should be combined to improve outcomes for any given patient. The first factor to consider is degree of protrusion, measured by the distance between a natural biting position and maximum protrusive jaw effort. Conventional practice is to advance the mandible between 60% to 80% of maximum voluntary protrusion. The second factor is the vertical dimension of occlusion (VDO) that can be incorporated into the oral appliance. To promote comfort, the VDO (space between the upper and lower teeth while protruding) is commonly reduced so the patient can achieve a good lip seal when the appliance is inserted. Limiting the vertical dimension between the upper and lower tray, however, reduces space in the oral cavity for the tongue to advance. This is particularly a problem in patients with large or scalloped tongues or those who sleep predominantly supine. FIG. 22 illustrates an example of a human tongue that exhibits scalloping along the edge of the tongue (2200). In comparison, FIG. 23 illustrates an example of a human tongue that does not exhibit scalloping along the edge. Increasing the VDO expands the space available for the genioglossus to advance and reduces the amount of protrusion needed for treatment efficacy. Optimally combining protrusion and VDO decreases the impact of OAT on bite change, the temporomandibular joint and associated muscle pain.
Oral appliances are typically fabricated by dental laboratories and made from materials which provide for two or more years of useful life. Fabrication of a custom appliance is dependent on a dentist providing impressions taken from the patient's upper and lower teeth as well as a bite registration for aligning the upper and lower teeth in the final appliance. Depending on the appliance, sub-millimeter protrusion adjustment can be attained based on thread pattern in order to extend the lower tray (teeth) beyond the upper tray (teeth). Because screw length and thread count limit the advancement range, the dentist is required to select a starting setting for the patient/appliance so that presumably the optimal advancement can be obtained without the need for appliance rework (i.e., removal and shifting of the adjustment mechanism to a more forward position to increase the protrusion range). Alternative protrusion methods include use of elastic bands to advance the lower tray, or inter-connecting slots where the upper (lower) trays fits into a limited number of advancement slots in the lower (upper) tray. These methods typically provide more limited options as to the number of advancement setting.
Appliances that do not provide advancement resolution of at least 1 mm tend to be less efficacious. A lack of advancement precision makes it difficult to select a starting setting that minimizes muscular pain causes by the initiation of nocturnal advancement. Limited incremental advancement also decreases the likelihood that an end point setting can be selected that optimizes therapeutic outcomes while also minimizing advancement that contributes to long term side effects (i.e., tooth movement, mandible repositioning, etc.)
Non-custom appliances are typically fitted to the teeth after modification to the material, e.g., thermal heating of a boil-and-bite appliance. Non-custom appliances can also be made with impression material to secure the teeth to the appliance, however, the limited life of the impression material (e.g., 30 days or less) suggest that these appliances are temporary in nature. Most non-custom or temporary appliances utilize low resolution protrusion methods.
Given the teeth are used to secure the OAT in place and the forces needed to advance the mandible are applied directly to the teeth, good periodontal health and dental hygiene is necessary for long term OAT use. Custom appliances have a smaller impact, while non-custom or boil-and-bite devices have a relatively greater impact on dental morbidity. The trays used to fabricate a non-custom oral appliance must either be manufactured in a range of sizes or be adjustable to accommodate the range of human dental arch widths. If the appliance does not properly accommodate arch width, the edges of the upper or lower tray will rub against the gums and cause discomfort or the appliance will be painful to wear for extended periods. It is not uncommon for patients who have snoring or OSA to clench and grind their teeth. Thus, oral appliances intended for sleep apnea patients should be designed to accommodate the forces applied by the clenching (bruxing) of the upper and lower teeth.
As mentioned previously, optimal OAT outcomes are dependent on combining protrusion with VDO. However, the VDO is not easily adjustable in many custom oral appliances once fabricated. Thus, it would be beneficial to determine the optimal oral appliance settings prior to the fabrication of a custom appliance. Providing a means for a physician to inexpensively conduct a trial and determine whether a patient responds to OAT prior to the fabrication of a custom appliance would also be beneficial. Providing a means whereby the determined oral appliance settings used in the trial that resulted in an efficacious outcome may be transferred to the custom appliance would also be beneficial.
Management of sleep disordered breathing present special perioperative challenges in patients due to the increased likelihood of respiratory depression and hypoxemia following surgery. Anesthesia, analgesia, and sedation drugs, commonly administered during and post-surgery and the recovery period, increase the severity of sleep disordered breathing by inhibiting the brain's capability to respond to obstructive breathing related hypoxemia or compromising the patency of the oropharyngeal dilator muscles. During initial recovery from general anesthesia, patients are nursed on their back and carefully monitored in the post-anesthetic recovery unit (PACU) until their self-supported ventilation and vital signs stabilize. Immediately following extubation and for the next few hours it is not uncommon for staff to manually advance the mandible forward (i.e., chinning) to keep the airway open in patients with obstructive sleep apnea.
Once patients leave the PACU the perioperative risks associated with obstructive breathing remain high due to the high levels of pain that mandate administration of analgesics (especially opioids) and changes in patterns of sleep architecture. REM-associated hypoxemic episodes is thought to increase about three-fold on the second and third postoperative nights. The rebound of slow wave sleep raises the arousal threshold, prolonging the time to arousal and allowing longer episodes of obstruction with deeper oxyhemoglobin desaturations. Because patients are routinely nursed on their hack, and gravity contributes to increased retrusion of the tongue and collapsibility of the airway, the incidence of obstructive breathing and severity of associated hypoxemia is increased independent of sleep stage. Even if supplemental oxygen is administered to reduce hypoxic exposure during obstructive breathing events, the physiological effects of repeated arousals (tachycardia and increased arterial blood pressure) add to the risk of perioperative complications. Because oxygen therapy and critical oxyhemoglobin saturation monitoring is generally discontinued prior to the REM-rebound, the highest perioperative mortality risk is not the day of surgery, or even the second day; it is on the third or fourth postoperative day. These risks continue in discharged patients who remain on narcotic pain medication. The most severe adverse outcome resulting from undiagnosed OSA is that the patient dies or becomes brain dead, the more common outcome is increased patient care cost resulting from complications that increase the length of the hospital stay or amount of time spent in the PACU or in critical care.
The American Society of Anesthesiologists recommends that all patients scheduled for general anesthesia be screened for undiagnosed OSA. One study estimated over 40% of those scheduled for general anesthesia have undiagnosed OSA based on a predictive analysis of questionnaire responses and overnight sleep study data. Thus, the feasibility for screening and potentially diagnosing patients with OSA prior to surgery was established. What has yet to be resolved is how to identify patients likely to have severe OSA and then how to mitigate OSA perioperative risk. Because most patients are unable to tolerate CPAP therapy when it is introduced post-operatively, for CPAP to be an effective perioperative intervention, patients must be identified a-priori and undergone a CPAP trial prior to admission. In most cases, this is simply not feasible. Given the risk of perioperative complications for those with untreated OSA and the ageing of the population it's likely the number of OSA-related adverse events will increasingly become a safety concern. Thus, an oral appliance that can be easily fitted and designed to manage the treatment of sleep apnea in a perioperative setting would be beneficial.